A method is described for reversibly inactivating small, precisely localized regions of brain tissue with injections of nanoliter quantities of the local anesthetic lidocaine hydrochloride. The injections are made through a combined recording-injection probe consisting of a glass micropipette onto whose outer surface is plated a metallic cylinder for recording extracellular action potentials. The recording cylinder, located a known distance from the pipette tip, picks up a continuous, large-amplitude, multiunit response which can be used to accurately position the tip according to physiological criteria. It also provides a means of determining the duration of the anesthetic block and estimating its spread. This devise has been used to selectively block 200-400 μm regions of individual laminae of the lateral geniculate nucleus centered within 50 μm of a retinotopically defined target site. The blocks last from 3 to 10 min and can be repeated many times at the same location. © 1979.
